In most motor vehicle powertrains, the heat generated due to operation of the engine is advantageously utilized, not only for cabin heating, but also for heating various exhaust gas emission control devices such as catalytic converters and particulate traps. While the heat generated during normal vehicle operation is sufficient for these purposes, the heat generated during idle operation can be insufficient, particularly during extended idle operation of a diesel engine. As a result, warming up the cabin during cold ambient temperatures can take an undesirably long time, and the exhaust gas temperature may be insufficient to activate the emission control devices. Accordingly, what is needed is a way of selectively and controllably increasing the engine temperature during idle operation.